ACtion Magazine - September 2014 - (Page 31)

Mechanical fan clutch diagnoses The engine cooling system is one of the ﬁrst and most basic of automotive systems that are taught in tech school, and rightly so. It's also one of the most frequently serviced systems in any vehicle. An often overlooked cause of overheating issues could begin with faulty engine driven thermostatic cooling fan clutches. Here's a great way to help diagnose these problems. We all know the normal ways to test these devices. Making sure the engine is turned off (and can't be started), grab hold of one of the fan blades, and try turning it by hand. You should feel resistance, but the fan should turn in both directions without freewheeling, and deﬁnitely should not be locked up. Next, check for wobble and end play by trying to move the fan blades towards and away from the engine. There should be no movement in this direction. Excessive wobble, freewheel or lock up indicates a likely faulty clutch in need of replacement. Here's another test you could try, but you're going to have to get yourself a handheld non-contact tachometer. They are relatively inexpensive, easy to use, and with enough practice and testing of many vehicles, can quickly let you know if there's an issue with the fan you've encountered. Place a piece of reﬂective tape onto the end of one of the fan blades (See Figure 1). Make sure you clean the blade ﬁrst so the reﬂective tape will stick and not ﬂy off. Next, start the vehicle, and get ready to measure. Hold I have heard of this being mentioned once or twice before. If you know of one, please let me know. I'd love to check it out (and mention it here in Cooling Corner). Otherwise, what I've found works best is practice. Using this technique on several different vehicles gives me a "database" of my own that I can reference. Now sure, I'm not going to ﬁnd the same readings on every one, most likely because of the differences in fan and pulley diameters, belt length, number of pulleys and base engine rpm speed differences amongst different vehicles. But generally speaking, you can ﬁgure out an average for your own purposes. ❆ MACS Staff By Steve Schaeber, MACS Technical Editor Figure 2: The red indicator light helps line up th tachometer. Steve Schaeber The MOST COMPLETE Tube & Hose Fabrication System available ANYWHERE! Duplicate Virtually ANY Tube or Hose Assembly METRIC or AMERICAN. Figure 1: Reﬂective tape on the blade is used to count fan RPM. your tachometer in such a position that you can get it to shine down onto that reﬂective tape. Then, you'll see the fan blade's rotational speed displayed on the tool in RPMs (See Figure 2). Through my own testing, I've found that a properly operating fan should spin somewhere around 1100 rpm when idling at normal operating temperature. However, I've also found a defective fan clutch that would spin at around 550 rpm. That's a pretty big difference from normal, but not unexpected on a 15-year-old vehicle. By the way, I did feel some wobble in the fan clutch shaft, but the rotational resistance really did feel ﬁne. In fact, had I not measured the rotational speed and compared it to a known good, I would not have condemned this clutch as a contributor to the overheating. Just how fast is a mechanical fan supposed to spin? Ever try looking up the speciﬁcations for this? It's not a commonly published spec, but CRIMP ALL types & brands of fittings using our Universal Crimper. Rebuild A/C & power steering hoses using our exclusive reclaiming ferrules. Custom build A/C & power steering fittings. BEND & form metal tubing from 3/16 to 1-1/4 inches. Convert standard to metric tubing using our up swage & down swage system. Make extreme & tight transition bends. FORM flares of all types including O-ring beads. O-ring beads in aluminum & steel tubing Up swage tubing to create braze joints. Reader Reply TUBES N' HOSES INTERNATIONAL 972-923-0766 E-mail: sales@tubesnhoses.com www.tubesnhoses.com September/October 2014 * ACtion 31 http://www.tubesnhoses.com http://www.macsw.org/imis15/MACS/Publications/ACtion_Reader_Reply/MACS/Publications/ACTION/ACtion_Reader_Reply.aspx?hkey=ac24bddb-c045-442a-813c-cbf05f88ac4d http://www.tubesnhoses.com

Table of Contents for the Digital Edition of ACtion Magazine - September 2014

Service Information
Aftermarket Truck A/C Installation
Outlook
Service Port
Leonard's Law
Virtual View
Last Watch
Member Profile
By the Numbers
Cooling Corner
Industry News
Association News
New Products

ACtion Magazine - September 2014